This invention relates to fuel injection in an internal combustion engine and, more particularly, to an improved fuel injection control system.
In one type of fuel injection control system in the prior art, the quantity of fuel injected into the engine's cylinders is controlled by varying the interval during which the fuel injectors are open. Usually, a plurality of sensors generate signals representing engine parameters indicative of the engine fuel requirement, such as absolute intake manifold pressure, engine speed, air temperature, and water temperature. Function generators individual to the sensors linearize the relationship between the sensed parameters and the fuel requirement. The outputs of the function generators are combined to form a composite signal, which is applied to a voltage controlled oscillator. The open interval of each fuel injector is determined by the time required for a counter to which the voltage controlled oscillator is connected counts a predetermined number of oscillator cycles. The higher the frequency of the voltage controlled oscillator, the faster the counter counts the predetermined number of cycles and the shorter is the open interval of the fuel injector. The conversion of the composite fuel requirement signal to a frequency requires a separate counter and corresponding control and logic circuitry for each fuel injector.